聚芴衍生物蓝光材料的合成及性质研究
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摘要
有机电致发光(OLED)是近年来国际上的一个研究热点。基于有机材料的电致发光技术可以应用于超薄平面显示和有机固体激光器等方面,在近20年来取得了飞速的发展,基本实现了红、绿、蓝三基色发光。绿色材料发展最快,基本达到了商业化实用阶段,而红色和蓝色发光材料的问题较多,特别是稳定、高效率的蓝光更具有挑战性。因而制备高效的蓝光器件一直是该领域的研究重点。为了实现稳定高效的蓝光发射,近年来,人们开发了大量的聚合物、寡聚物体系。但是能够满足实用要求的蓝光高分子材料却非常有限。而聚芴(polyfluorene, PF)作为一种具有刚性平面联苯结构的化合物,由于具有宽的能隙、高的发光效率和结构上易于修饰等特点,是一类受到各方面广泛关注的蓝光材料。
但聚芴类蓝光材料的一个缺点是薄膜在空气中退火或者器件在长时间运行后会出现长波发射,严重影响其综合电致发光性能。目前有些人认为是由分子间激基缔合物引起的,但更多的观点是认为聚芴的9位被氧化生成芴酮导致该长波发射。本论文针对聚芴容易被氧化生成芴酮这一问题,在聚芴主链中引入强吸电子性的2,5-二氟苯,从而降低芴环的电子云密度,使其9位被氧化的可能性大大降低。也针对吸电子基团的过多引入会导致其发光效率和电子传输能力都有所降低,调节了2,5-二氟苯在聚芴中的含量,合成了一系列含不同比列的2,5-二氟苯的聚芴衍生物。通过对比,以期待得到荧光量子效率和电子传输能力都比较好的纯蓝光材料。本文合成了2,7-二溴-9,9-二辛基芴、9,9.二辛基-2,7-芴双硼酸酯、1,4-二溴-2,5-二氟苯三种单体,以不同的比例经过Suzuki缩聚合成一系列的聚合物。产物经过溶解-沉降、索式提取等方法提纯,并通过GPC和1H NMR以及元素分析等手段鉴定了分子量分布和分子结构。
该一系列聚合物在普通的有机溶剂里都具有很好的溶解性,可以通过旋涂或喷墨等方法来制备薄膜和器件。利用紫外可见吸收光谱及荧光光谱,发现相对于聚芴,这一系列聚合物的紫外吸收位置及荧光发射位置都发生了蓝移,且荧光量子效率有较小降低。
该一系列聚合物的固体薄膜在空气中升温至100℃时仍具有较好的热稳定性,这表明在聚芴中引入了具有吸电子基团的2,5-二氟苯可以大大改善其光谱稳定性,是一系列荧光量子效率较高、蓝光光谱稳定、具有适当的电子传输能力的纯蓝光材料。
As a novel displaying technique with promising application in flat-panel displays, organic light-emitting diodes (OLEDs) have received particular attention by virtue of the following properties:direct current driving, self-luminous, small volume, fast response, full color emission, wide view angle and simple manufacture techniques. Among the three primary colors of OLEDs, the green light-emitting materials have achieved a practical level while the red and blue ones still lag behind them especially the blue materials with high stability and efficiency. Nowadays to develop blue emitters with high performance has been the focus of the research. The polyfluorene (PF) with rigid planar biphenyl structure is just enough to supply the demand due to its wide energy gap, high fluorescent quantum yield and ease to be modified.
However, the blue light-emitting material of polyfluorene have a drawback that will cause long-wave emission if annealed in air or operation in air for a long time, which seriously affect the comprehensive performance of the electroluminescence. Currently, it is widely accepted that the 9-C position of fluorine ring was oxidized to fluorenone, which give rise to the long-wave emission. In this dissertation, in order to improve the spectra stability of polyfluorenes, we introduce the strong electron-withdrawing 2,5-difluorobenzene to the backbone of polyfluorene, with the expectation to reduce the electron density on fluorene ring and hence to greatly reduce the possibility of fluorine oxidation. It is generally accepted that large amount of electron-withdrawing substituent will decrease the luminescent efficiency and charge mobility. In order to optimize the fluorescent quantum yield, solubility and charge-transporting ability of the resulted polyfluorenes at the same time, therefore, we tuned the contents of the difluorobenzene group and prepared a series of copolymer with different ratio of 2,5-difluorophenyl. The products were purified by the method of dissolution-deposition and soxhlet extraction. The distribution of molecular weight and molecular structure was identified by GPC,1HNMR spectroscopy and elemental analysis.
This series of polymers have good solubility in common organic solvents. So it is possible to prepare films and devices by solution methods such as spin coating or ink jet printing. The spectroscopy study exhibited that the UV absorption and fluorescence spectra of this series of polymers had a blue shift in comparison with those of the parent polyfluorene, and the fluorescence quantum yields had a small decrease.
The films of the obtained polymers were annealed in air at 100℃for 2 hours to detect the emission spectra stability. No green emission was observed after the annealing, suggesting that these novel polyfluorenes with difluorobenzene units on backbone are not prone to air oxidation.
但聚芴类蓝光材料的一个缺点是薄膜在空气中退火或者器件在长时间运行后会出现长波发射,严重影响其综合电致发光性能。目前有些人认为是由分子间激基缔合物引起的,但更多的观点是认为聚芴的9位被氧化生成芴酮导致该长波发射。本论文针对聚芴容易被氧化生成芴酮这一问题,在聚芴主链中引入强吸电子性的2,5-二氟苯,从而降低芴环的电子云密度,使其9位被氧化的可能性大大降低。也针对吸电子基团的过多引入会导致其发光效率和电子传输能力都有所降低,调节了2,5-二氟苯在聚芴中的含量,合成了一系列含不同比列的2,5-二氟苯的聚芴衍生物。通过对比,以期待得到荧光量子效率和电子传输能力都比较好的纯蓝光材料。本文合成了2,7-二溴-9,9-二辛基芴、9,9.二辛基-2,7-芴双硼酸酯、1,4-二溴-2,5-二氟苯三种单体,以不同的比例经过Suzuki缩聚合成一系列的聚合物。产物经过溶解-沉降、索式提取等方法提纯,并通过GPC和1H NMR以及元素分析等手段鉴定了分子量分布和分子结构。
该一系列聚合物在普通的有机溶剂里都具有很好的溶解性,可以通过旋涂或喷墨等方法来制备薄膜和器件。利用紫外可见吸收光谱及荧光光谱,发现相对于聚芴,这一系列聚合物的紫外吸收位置及荧光发射位置都发生了蓝移,且荧光量子效率有较小降低。
该一系列聚合物的固体薄膜在空气中升温至100℃时仍具有较好的热稳定性,这表明在聚芴中引入了具有吸电子基团的2,5-二氟苯可以大大改善其光谱稳定性,是一系列荧光量子效率较高、蓝光光谱稳定、具有适当的电子传输能力的纯蓝光材料。
As a novel displaying technique with promising application in flat-panel displays, organic light-emitting diodes (OLEDs) have received particular attention by virtue of the following properties:direct current driving, self-luminous, small volume, fast response, full color emission, wide view angle and simple manufacture techniques. Among the three primary colors of OLEDs, the green light-emitting materials have achieved a practical level while the red and blue ones still lag behind them especially the blue materials with high stability and efficiency. Nowadays to develop blue emitters with high performance has been the focus of the research. The polyfluorene (PF) with rigid planar biphenyl structure is just enough to supply the demand due to its wide energy gap, high fluorescent quantum yield and ease to be modified.
However, the blue light-emitting material of polyfluorene have a drawback that will cause long-wave emission if annealed in air or operation in air for a long time, which seriously affect the comprehensive performance of the electroluminescence. Currently, it is widely accepted that the 9-C position of fluorine ring was oxidized to fluorenone, which give rise to the long-wave emission. In this dissertation, in order to improve the spectra stability of polyfluorenes, we introduce the strong electron-withdrawing 2,5-difluorobenzene to the backbone of polyfluorene, with the expectation to reduce the electron density on fluorene ring and hence to greatly reduce the possibility of fluorine oxidation. It is generally accepted that large amount of electron-withdrawing substituent will decrease the luminescent efficiency and charge mobility. In order to optimize the fluorescent quantum yield, solubility and charge-transporting ability of the resulted polyfluorenes at the same time, therefore, we tuned the contents of the difluorobenzene group and prepared a series of copolymer with different ratio of 2,5-difluorophenyl. The products were purified by the method of dissolution-deposition and soxhlet extraction. The distribution of molecular weight and molecular structure was identified by GPC,1HNMR spectroscopy and elemental analysis.
This series of polymers have good solubility in common organic solvents. So it is possible to prepare films and devices by solution methods such as spin coating or ink jet printing. The spectroscopy study exhibited that the UV absorption and fluorescence spectra of this series of polymers had a blue shift in comparison with those of the parent polyfluorene, and the fluorescence quantum yields had a small decrease.
The films of the obtained polymers were annealed in air at 100℃for 2 hours to detect the emission spectra stability. No green emission was observed after the annealing, suggesting that these novel polyfluorenes with difluorobenzene units on backbone are not prone to air oxidation.
引文
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[13]K.Imaizumi, K.Kaneko, T.Mori,et al., Analysis of electroluminescence mechanisms in N,N'-disphenyl-N,N'-bis(3-methylphenyl)-1,1'-disphenyl-4,4'-diamine/hydroxy quinoline aluminum bilayer organic light-emitting diode by bipolar hopping conduction[J]. J. Appl. Phys.,2002,41(1):366-373.
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[27]J.Kido, Y.Iizumi, Fabrication of highly efficient organic electroLuminescent devices[J]. Appl. Phys. Lett.,1998,73,2721-2723.
[28]M.Brinkmann, G.Gadret, M.Muccini, C.Taliani, Correlation between molecular packing and optical properties in different crystalline polymorphs and amorphous thin films of mer-Tris(8-hydroxy quinoline)aluninum[J],.J. Am. Chem. Soc.,2000,122,5147-5157.
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[2]黄春晖,李富友,黄岩谊.光电功能超薄膜[M].北京：北京大学出版社,2001.
[3]Bevacqua S F. Cohenrent (Vistble) Light Emission From Ga(As1-xPx) Junctions[J]. Appl. Phys. Lett., 1962,1:82-83.
[4]M.Pope, H.P.Kallmann, P.Magnante. Electroluminescence in organic crystals[J]. J. Chem. Phys.,1963, 38:2042-2043.
[5]P.S.Vincett, W.A.Barlow, R.A Hann, et al. Electrical conduction and low voltage blue electroluminescence in vacuum-deposited organic films[J]. Thin Solid Films,1982,94:171-174.
[6]R.H.Partidge. Electroluminescence from polyvinylcarbazole films:3 Electroluminescent devices[J]. Polymer,1983,24:746-752.
[7]C.W.Tang, S.A.Van Slyke. Organic electroluminescent diodes[J]. Appl. Phys. Lett.,1987,51(12): 913-915.
[8]C.W.Tang, S.A.Vanslyke, C.H.Chen. Electroluminescence of doped organic thin films[J]. J. Appl. Phys.,1989,65:3610-3616.
[9]C.Adachi, T.Sutsui and S.Saito.Blue light-emitting organic electroluminescent devices[J]. Appl.Phys.Lett.,1990,56:799-78
[10]J.H.Burroughes, D.D.Bradley, A.R.Brown, et al..Light-emitting diodes based on conjugated polymer [J]. Nature,1990,347:539-542
[11]徐清,王丽,余兴莲等。有机电致磷光材料的研究新进展[J].光谱实验室,2006,23：772-777
[12]Y.Sun, N.C. Giebink, H. Kanno, B. Ma, M. E. Thompson, S. R. Forrest. Management of singlet and triplet excitons for efficient white organic light-emitting devices[J]. Nature,2006,440,908.
[13]K.Imaizumi, K.Kaneko, T.Mori,et al., Analysis of electroluminescence mechanisms in N,N'-disphenyl-N,N'-bis(3-methylphenyl)-1,1'-disphenyl-4,4'-diamine/hydroxy quinoline aluminum bilayer organic light-emitting diode by bipolar hopping conduction[J]. J. Appl. Phys.,2002,41(1):366-373.
[14]J.Mort, G.Prister., Photoelectronic properties of disordered organic solids:molecularly-doped polymers[J]. Polym.-Plast. Tech. Eng.,1979,12(2):89-140.
[15]李亨.颜色技术原理及其应用[M].北京：科学出版社,1994.
[16]R.D.Scurlock, J.Wang, P.R.Ogilby et al. Singlet oxygen as a reactive interme-diate in the photodegradation of an electroluminescent polymer[J]. J. Am. Chem. Soc.,1995,117,10194-10202
[17]Z.Shen, P.E.Burrows, V.Bulovic,et al., Three-color,tunable,organic light-emitting devices[J].Science, 1997,276,2009-2011.
[18]谈春霞,萧泰.有机小分子及金属有机配合物电子传输材料的研究进展[J].西北师范大学学报(自然科学版),2005,41(6)：94-97.
[19]李文连.用于有机EL器件的电极材料[J].液晶与显示,2000,15(2)：108-113.
[20]马昌期,王雪松,张宝文等.有机电致发光空穴传输材料研究进展[J].化学进展,2003,15(6)：497-503.
[21]U.Mitschke, P.Buerle, The electroluminescence of organic materials[J]. J. Mater. Chem.,2000,10, 1471-1507.
[22]Y.Shirota., Organic materials for electronic and optoelectronic devices[J]. J. Mater. Chem.,2000,10:
1-25.
[23]黄春辉,李富友,黄维.有机电致发光材料与器件导论[M]。复旦大学出版社,2005.
[24]Y.Shirota, Y.Kuwabara, H.Inada., Multilayered organic electroluminescent device using a novel starburst molecule,4-4'-4"tris(3-methylphenylphenylamino)triphenylamine,as a hole transport material[J]. Appl. Phys. Lett.,1994,65,807-809.
[25]C.Adachi, S.Tokito, T.Tsutsui., Electroluminescence in organic films with three-layer structure[J]. Jpn. J. Appl. Phy.,1988,27, L269-271.
[26]C.W.Ko, Y.T.Tao.,9,9-Bis{4-[di-(p-biphenyl)aminophenyl]}fluorene:a high Tg and efficient hole-transporting material for electroluminescent devices [J]. Synth. Met.,2002,126,37-41.
[27]J.Kido, Y.Iizumi, Fabrication of highly efficient organic electroLuminescent devices[J]. Appl. Phys. Lett.,1998,73,2721-2723.
[28]M.Brinkmann, G.Gadret, M.Muccini, C.Taliani, Correlation between molecular packing and optical properties in different crystalline polymorphs and amorphous thin films of mer-Tris(8-hydroxy quinoline)aluninum[J],.J. Am. Chem. Soc.,2000,122,5147-5157.
[29]P.Strohriegl, J.V.Grazulevicius., Charge-transporting molecular glasses[J]. Adv. Mater.,2002, 14,1439-1452.
[30]H.E.Katz, A.K Lovinger, J.Hohnson, A Dodabalapur et al. Asoluble and air-stable organic semiconductor with high electron mobility[J]. Nature,2000,404,478-480.
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